Mechanisms underlying the diverse pathogenic effects of HLTV-I infection are not well understood. The present studies are designed to investigate interactions between viral products and host cell processes. Previous studies in the LIG involve two HTLV-I infected rabbit cell lines RH/K30 and RH/K34. Upon injection into rabbits, RH/K34 causes lethal experimental leukemia and RH/K30 mediates asymptomatic infection. Molecular clones, K30p and K34p, were derived from the cell lines and functional studies have shown that the molecular clone K30p mediates persistent infection both in vitro and in vivo, whereas K34p does not. The pX region of K30 was shown to play a central role in the ability of the molecular clones to produce persistent infection. Sequence differences between K30p and K34p include two nucleotide substitutions in the pX region that produce replacement substitutions in p13 and p30 products. Clones containing either of the individual pX region substitutions corresponding to the K34 sequence transiently produced low levels of virus. The focus of these studies is to compare functions of p13 and p30 from these two HTLV-1 molecular clones. The yeast two-hybrid system was employed to identify cellular proteins that physically interact with p13 and p30 from K30p and K34p.A cDNA library prepared from RH/K30 was screened with p13 from K30p or p13 from K34p as bait. Two clones, designated C44 and C254 specifically interacted with p13K34; no clones were isolated that interact with p13K30 or with the irrelevant protein, bicoid. Both C44 and C254 were sequenced and compared with sequences in the data bank using BLAST analyses to identify the proteins that they encode. C44 encodes a 188 amino acid polypeptide that shows 88% identity with a human protein of unknown function and significant homologies with members of the nucleoside monophosphate kinase (NMPK) superfamily. C44 RNA expression was detected in a variety of B and T lymphocyte cell lines but was not observed in freshly isolated peripheral blood lymphocytes. C254 encodes the C terminal region of ABP-280 which is a prominent component present in the cytoskeleton of many different cell types. Northern blot analysis showed similar levels of C254 (ABP-280) RNA expression in RH/K30 and RH/K34. However, Western blots of protein from RH/K30 and RH/K34 using a monoclonal antibody to non-muscle filamin (ABP-280) revealed that ABP-280 protein was detected only in RH/K34 cells.